Conventional time domain multiple access (TDMA) satellite communication networks employ multiple radio stations which communicate through an earth satellite repeater by transmitting time-synchronized bursts of radio energy relative to the repeater and which receive a time multiplex composite of bursts containing corresponding modulated information from the repeater. In TDMA operations, multiple ground stations associated with radio signaling nodes transmit bursts of time-concentrated information signals on a shared carrier frequency spectrum and receive the same information signals after repetition by the satellite repeater on a shifted carrier frequency spectrum. Each ground station is assigned a particular time slot in a continuum of recurrent frames for transmission of its bursts and for the reception of its own bursts and the bursts of other stations. The bursts interleave at the satellite in close time formation without overlapping. Each earth station includes connections to incoming digital lines originating from terrestrial sources. These input lines are respectively connected to digital data ports on a satellite communications controller (SCC) at the station.
The terrestrial sources typically have a variety of data rates which are different from the basic TDMA transmission rate of the SCC. Prior art systems have attempted to compensate for differences in data rates of sources by inserting stuff bits in the transmitted messages. One example of the prior art is directed to an expansion/compression and elastic buffer combination which is used for compensating for the variability of data rates by adding or subtracting dummy or stuffing bits when necessary to provide the data output rate of the terrestrial source at the basic TDMA transmission rate of the SCC. The reading out of the data port occurs once every frame without regard for the number of bits which have been received from the terrestrial source in the data port and appending a code word which determines the number of stuffing bits to add to the data read-out from the data port so as to make up the total number of bits necessary to maintain the basic TDMA transmission rate for the SCC. Such techniques for compensating for differences in the data rate of a terrestrial source from the basic TDMA transmission rate of the SCC are wasteful of the transmission bandwidth in a TDMA satellite communications system.